A commonly posed question from the newsgroups: “what software can do bit-for-bit copies?
There isn’t any. If it helps to have a (convenient albeit somewhat inaccurate) mental image, picture a long string of bits arranged in a spiral. There are bits at the start of the spiral that you can’t copy (the lead-in area), there are bits outside the spiral that you can usually copy if you request them (“raw” MODE-1 CD-ROM ECC and sector goop), and there are bits *under* the spiral that are blurry and hard to see (the subcode data). Making a “bit-for-bit” copy of a disc would require reading the data at the lowest possible level, something that no production CD-ROM drive is capable of doing. Even if it were possible, there aren’t any CD recorders that can write that sort of data. Because of these limitations, you have to read a sector of data as a sector of data, not as a collection of frames scattered over half the circumference of the disc. You can read the sector in “raw” mode, scan for index markers, and try to extract CD+G data tucked into the R-W subcodes, but there’s a good c
” The expectation is software that can make an exact copy of the original. There isn’t any. If this seems counter-intuitive, bear in mind that discs hold digital data on an analog medium. While “bits” may be what you read from the drive, at some point those bits have to be stored as marks or indentations on a piece of polycarbonate. The “low-level” modes, such as “raw DAO-96”, are actually pretty high level. By the time you’ve got 2352-byte sectors and 96-bits of subcode channel data, the drive has converted optical reflections to an analog signal, converted the analog signal to digital bits, combined individual bits into 24-byte frames, applied error correction, and assembled the frames into the data you see. When you’re writing a sector, all that stuff happens on the way out, too, and there’s no way for CD recording software to control it. What’s more, there are copy protection features, such as *physically* damaged blocks, that a recorder isn’t generally capable of writing. Other tr
